Neurophysiologic monitoring has become an increasingly important adjunct to surgical procedures in which neural tissue may be at risk. Spinal surgery, in particular, involves working close to delicate neural tissue in and surrounding the spine, which can be damaged in any number of different ways. Because of the complex structure of the spine and nervous system, no single neurophysiologic monitoring technique has been developed that adequately assesses the risk to nervous tissue in all situations. For this reason, two or more complex techniques are often used concurrently during surgery. Examples of such techniques include free-run (spontaneous) electromyography (EMG), stimulated (evoked) EMG, and motor evoked potentials (MEP).
Free-run EMG, stimulated EMG, and MEP testing have historically required specially-trained neurophysiologists to perform the testing. Even though performed by specialists, interpreting the complex waveforms in this fashion is nonetheless disadvantageously prone to human error and can be disadvantageously time consuming, adding to the duration of the operation and translating into increased health care costs. Even more costly is the fact that the neurophysiologist is required in addition to the surgeon performing the spinal operation.
Surgeon-operable systems have attempted to overcome some of these difficulties. However, performing multiple techniques simultaneously can still be a challenge because optimal signal response characteristics may vary between the different techniques, but the response activity associated with one technique may comingle with the response activity associated with another technique. For example, performing free-run EMG testing during a posterior lumbar fusion procedure is advantageous in that it provides a surgeon with continuous, real-time feedback regarding the health of the nerve roots during the procedure. Additionally, static pedicle screw testing is also advantageous in the same procedure because it can verify proper positioning of the screw within the pedicle. However when performing both techniques simultaneously, background noise and/or neurophysiologic activity from the free-run EMG technique may comingle with the compound muscle action potential (CMAP) responses evoked by, for example, the static pedicle screw testing. Such comingling could affect the static pedicle screw testing results in such a way as to lead to a false positive result.
The system and methods described herein are directed at eliminating, or at least reducing, the effects of the above-described problems.